1. Field of the Invention
The present invention is generally directed to a method of preparing a board for use as siding. More particularly, the invention relates to a high speed application of a polyurethane-based liquid coating onto a cellular polyvinylchloride (“cellular PVC”) board, wherein the resulting coated cellular PVC board exhibits improved characteristics including reduced warping and bowing, and improved adhesion, and abrasion and mar resistance.
2. Background of the Invention
Difficulties have been encountered in providing and applying durable protective coatings to siding, wherein, among other things, such siding is used to cover the exteriors of buildings, homes, and lawn and garden furniture, for example. Part of the problem with formulating an effective coating lies in the inherent nature of the substrate used to form the siding. That is, when exposed to its working environment, which includes adverse and fluctuating environmental conditions, such as, heat, cold, ultraviolet radiation, moisture, wind, snow, salt spray, particle impingement, smog, and the like, the substrate tends to expand, contract, and/or flex. Consequently, the constant stress placed on the substrate due to changing environmental conditions and/or handling, causes the prior art coatings to easily peel, chip, blister or otherwise separate from the substrate, necessitating frequent and costly scraping and recoating operations. Additionally, prior art coatings on interior components also deteriorate as a result of the substrate and/or the coating's exposure to wide humidity changes, abrasions, sudden impacts, and contact with corrosive fluids, dirt, grime and the like.
Many of the foregoing durability problems can be attributed to the unsatisfactory adhesion of the coating to the substrate surface due to such coatings not having sufficient bonding with the unique surface of the substrate, as well as proper flexibility consistent with the dynamics of the substrate, balanced with sufficient hardness characteristics.
Accordingly, there has been a need for a coating process which can tightly and durably bond the coating to the cellular PVC substrate and which will resist peeling, blistering and other separation under adverse conditions, including highly variable temperature and humidity conditions. The application process would allow the coating to remain flexible and expandable and resist abrasion and impact. Given all of the above, the coating must possess, most importantly, optimal viscosity and atomization characteristics that lend themselves to a high speed application process thereby maximizing the efficiency of the coated cellular PVC board's manufacture.
In addition to producing a coated substrate that wears better, both in terms of function and aesthetics, greater adhesion and flexibility on the part of the coating would also provide for a greater selection of colors which could be used to create the coating. That is, conventional coatings used to coat siding substrates, are conventionally limited to light colors, i.e., white, light grays, light tans, light beiges, and the like, as these coatings absorb less heat as compared to darker colors, and, hence, result in lower degrees of substrate expansion and splintering as would occurs when a darker color is used to form the coating. Accordingly, what is also needed is a siding material that can come in a myriad number of colors, including both light and dark colors, without concerns of bowing and warping when the siding material is exposed to its environmental conditions.